Electronic toll collection (“ETC”) systems are commonly used to facilitate the collection of a toll from a moving vehicle traveling on a toll-roadway.
In a typical ETC system, a series of antennas are mounted near the roadway to provide overlapping coverage zones. Radio frequency (“RF”) transponders are mounted on or within a vehicle to communicate with the antennas as they pass through the coverage zone for the antenna. A roadside Automatic Vehicle Identification (“AVI”) reader causes each antenna to transmit an RF trigger or wakeup signal within the coverage zone. A transponder passing through the coverage zone detects the wakeup or trigger signal and responds with its own RF signal. The response signal typically includes information stored in a transponder memory, such as an identification number associated with the transponder. In some systems, the roadside reader may be connected to a vehicle detector and imaging system which permits vehicles to be detected, classified, and photographed, and the license plate numbers analyzed in order to permit the operator of the toll system to apply appropriate charges to the owner of the vehicle.
The AVI reader typically includes software for determining a probable lane position of the vehicle. After the AVI reader has read the data transmitted by the transponder, the reader typically transmits updated information to the transponder using an antenna having a coverage zone which includes the probable position of the vehicle, as determined by the software for determining the probable lane position of the vehicle. For example, the reader may transmit a timestamp and/or a lane and Plaza ID identifying the lane and plaza which the transponder has passed through. When the transponder receives the updated information, it typically stores the updated information in the transponder memory.
In some circumstances, a transmission problem may occur resulting in a failed programming attempt. For example, the transponder may not receive a signal if the transponder has traveled outside of the coverage area of the antenna used to transmit the programming signal. Interference caused by other electrical devices may also result in the programming signal or a portion of the programming signal not being received by the transponder. A transmission error may also occur due to reflections, multipath and the attenuation of the RF programming signal as it passes from the exterior of the vehicle to the interior of the vehicle where the transponder is typically located.
It is therefore desirable to provide an improved method and system for communicating with a transponder located in a moving vehicle in a toll roadway.